Solar radiation includes about 5% ultraviolet (UV) radiation, wavelength of which is between 200 nm and 400 nm. It is further classified into three regions: from 320 to 400 nm (UV-A), 290 to 320 nm (UV-B) and from 200 to 290 nm (UV-C). A large part of UV-C radiation is absorbed by the ozone layer. Scientific studies have indicated that exposure to UV-A and UV-B radiation for short period causes reddening of the skin and localized irritation, whereas continued and prolonged exposure can lead to sunburn, melanoma and formation of wrinkles and age spots. It is also reported that UV radiation causes significant damage to hair. Therefore, it is desirable to protect the skin and other keratinous substrates of the human body from the harmful effects of both UV-A and UV-B radiation, in addition to increasing the SPF protection.
Various cosmetic preparations have been reported for preventing and/or protecting the skin from harmful effects of ultraviolet radiation. Numerous organic sunscreen agents capable of absorbing UV-A rays are reported in the field of cosmetics amongst which a particularly useful sunscreen is t-butylmethoxydibenzoylmethane (a.k.a avobenzone, also sold as Parsol 1789). Many UV-B sunscreens are also known and approved for safe use in personal care compositions for protection from UV-B radiation. Many cosmetic manufacturers prefer to include both UV-A and UV-B sunscreens in photoprotective compositions so as to provide protection over the entire range of UV radiation.
Thus, cosmetic manufacturers aim to provide consumers with products having better and better sun protection. One of the ways of achieving this is to incorporate higher and higher levels of UV-A and UV-B sunscreens. One disadvantage of this approach is the high cost associated with incorporation of high levels of sunscreens which are expensive. Further, there are safety and regulatory limitations on the upper limit of incorporation of these sunscreens. Finally, sensory properties are also altered on incorporation of sunscreens, particularly when the amounts of sunscreens are increased. Many topical compositions have a unique sensory feel that consumers come to recognize and love and associate with the particular brand or composition. As the knowledge of the harmful effects of UV exposure developed, it became desirable to improve UV-A and UV-B protection substantially, without increasing levels of UV-A and UV-B protection. This is not trivial, particularly for non-solid personal care formulations, since sunscreens tend to have high impact on viscosity, drying behavior, and other tactile and sensory characteristics of the formulation. It is critical to preserve the sensory profile of the composition while achieving a substantial UV-A and UV-B boost. If the feel of the formulation is altered, consumer loyalty may quickly change The present inventors have unexpectedly determined that by virtue of incorporating tricyclodecane amides along with UV-A and UV-B sunscreens, a significant boost in UV-A and UV-B protection, and in SPF, can be achieved. The present inventors further unexpectedly determined that tricyclodecane amides suppress sebum production, which is advantageous in photoprotection compositions which tend to contain relatively high amounts of oil—excess sebum exacerbates oily feel of such compositions.
Tricyclodecane derivatives, and in some cases tricyclodecane amides, have been described. See for instance Kilburn et al., U.S. Pat. No. 8,053,431B2; WO2004/089415A2 (Novo Nordisk NS); WO2004/089416A2 (Novo Nordisk NS); Narula et al., U.S. Pat. No. 4,985,403; Mathonneau, US 2006057083; WO06/119283 (Hunton & Williams LLP); WO08/054144 (Amorepacific Corporation); Other amides have been used for boosting UV protection—see e.g. US2011/0104087 (Unilever), but they did not achieve the improvement for both the UV-A and UV-B, only UV-A.